Calling program functions

You can use this variant of the print command if you want to
execute a function from your program, but without cluttering the output
with void returned values. If the result isn't void,
it's printed and saved in the value history.

callexpr

Evaluate the expression expr without displaying
void returned values.

A user-controlled variable, call_scratch_address, specifies
the location of a scratch area to be used when GDB calls a
function in the target. This is necessary because the usual method
of putting the scratch area on the stack doesn't work in systems that
have separate instruction and data spaces.

Note:
In a multithreaded programs, calling a function may allow multiple threads to run.